Some applications use an external hardware device that connects to the USB port to authorize the use of the software on your Macintosh. This device is commonly referred to as a "dongle."
If your application is having trouble locating a dongle that is plugged into a display or keyboard, try plugging it into one of the USB ports on the CPU. This should allow your application to more easily locate the dongle and authorize use of your software.
Note: If issues persist on the Mac Pro's USB ports, refer to the third-party vendor that provided the dongle.